Definition, Etiology, Epidemiology of Down Syndrome

Definition of Down Syndrome

Down syndrome is a common birth defect that is usually due to an extra chromosome 21 (trisomy 21). Down syndrome causes mental retardation, a characteristic facial appearance, and multiple malformations. It occurs most frequently in children born to mothers over age 35. 

Etiology of Down Syndrome

Down syndrome is caused by the following 3 cytogenic variants:

• Three full copies of chromosome 21• Chromosomal translocation that results in 3 copies of the

critical region for Down syndrome• Mosaicism

The etiology of down syndrome:1. Genetic2. Radiation 3. Infection 4. Auto-imun5. Age of mother6. Age of father (parent’s age).

Epidemiology

Globally, as of 2010, Down syndrome occurs in about 1 per 1000 births[and results in about 17,000 deaths. More children are born with Down syndrome in countries where abortion is not allowed and in countries where pregnancy more commonly occurs at a later age. About 1.4 per 1000 live births in the United States[ and 1.1 per 1000 live births in Norway are affected. In the 1950s, in the United States, it occurred in 2 per 1000 live births with the decrease since then due to prenatal screening and abortions. The number of pregnancies with Down syndrome is more than two times greater with many spontaneously aborting. It is the cause of 8% of all congenital disorders

Maternal age affects the chances of having a pregnancy with Down syndrome. At age 20, the chance is one in 1441; at age 30, it is one in 959; at age 40, it is one in 84; and at age 50 it is one in 44. Although the probability increases with maternal age, 70% of children with Down syndrome are born to women 35 years of age and younger, because younger people have more children. The father's older age is also a risk factor in women older than 35, but not in women younger than 35, and may partly explain the increase in risk as women age